Calibration of the San Marco airglow-solar spectrometer instrument in the extreme ultraviolet

The San Marco 5 carried the airglow-solar spectrometer instrument (ASSI). This 18-channel spectrometer measured the solar and terrestrial radiation in the wavelength region between 20 and 700 nm for 9 months in 1988. The ASSI extreme ultraviolet (EUV) channels showed significant sensitivity changes during the mission. The sensitivity changes of the EUV channels are quantified by comparing ASSI solar EUV irradiance measurements to the solar EUV irradiance derived from a solar proxy model. A sensitivity change model is developed that shows that exponential curves can adequately describe the sensitivity changes of the ASSI optics and detectors. The November 10 calibration parameters and the sensitivity change model can be used to derive the EUV terrestrial airglow brightness for the time period of the ASSI mission. Analysis of the solar Lyman-α irradiance measured by the ASSI, the solar mesospheric explorer (SME), and the upper atmosphere research satellite (UARS) has led to a revised Lyman-α irradiance for the San Marco mission. For example, the ASSI November 10, 1988, Lyman-α measurement is 5.3×10¹¹ photons cm^-2 s^-1 versus the reported SME measurement of 3.35×10¹¹ photons cm^-2 s^-1.